1. Field of the Invention
The present invention relates to a semiconductor device and in particular, to a semiconductor device including an I/O block of the ball grid array (BGA) configuration.
2. Description of the Related Art
Recently, with increase of the number of pins and reduction of size of a semiconductor package, the conventional semiconductor package having a plurality of pin terminals tends to be replaced by a semiconductor package of the BGA configuration (called chip size package (CSP) or BGA package) as disclosed in, for example, Japanese Patent Publication 10-261737.
In this case, the semiconductor package (semiconductor device) normally includes a plurality of wiring layers (inner leads) layered via an insulation layer on a semiconductor chip. Each of the wiring layers constituting a part of the semiconductor package is provided with a land block (I/O region) of the chip side, to which solder balls are attached, thus constituting a semiconductor package (BGA package) of the ball grid array (BGA) structure.
When mounting the substrate on the package, the wiring layers of the semiconductor package side including the ball grid array (BGA) and the corresponding wiring of the substrate side are entirely heated, so that the respective circuits are connected via the solder balls.
However, in the aforementioned conventional example, as the BGA package and the substrate have different coefficients of thermal expansion, cracks are caused in the solder balls due to a temperature stress when subjected to a sudden temperature change. Moreover, because the solder balls are attached to flat planes of the substrate, the attachment strength between the solder ball and the substrate is insufficient and an open failure is easily caused by a physical stress such as vibration and shock.
It is therefore an object of the present invention to provide a semiconductor device capable improving the attachment strength between a land block of the chip side and effectively suppressing growth of a solder ball crack caused by a temperature stress.
In the order to achieve the aforementioned object, the present invention provides a semiconductor device of the BGA (ball grid array) package type comprising: a semiconductor chip; a plurality of wiring layers (inner leads) arranged on the semiconductor chip via an insulation layer, each of the wiring layers, having a chip-side land block as a signal I/O region; a circuit substrate having a plurality of wiring lines; and a plurality of solder balls each to be arranged on the chip-side land block for connecting the wiring layers to corresponding wiring lines on the circuit substrate; wherein each of the chip-side land blocks has a protrusion block extending into the solder ball toward a corresponding wiring line in the substrate.
For example, when the semiconductor device is placed under a severe temperature change, a crack is generated in the vicinity of a boundary between a solder ball and an inner lead of a corresponding chip-side land due to a stress caused by a difference of coefficients of the thermal expansion of the chip and the circuit substrate and applied in the horizontal direction in the solder ball (direction along a surface of the substrate). However, the inner stress when reaching the land protrusion block, proceeds along the land protrusion block which is different from the aforementioned direction. Thus, the stress is dispersed in indifferent directions. This effectively suppresses generation and growth of a crack.
Furthermore, the land protrusion block significantly increases the surface area of the chip-side land block, which in turn increase the attachment area between the chip-side land block and the solder ball, thereby significantly increasing the attachment strength.
Here, the land protrusion block may include a circular protrusion. Moreover, the land protrusion block may include a columnar protrusion surrounded by the circular protrusion surrounding. Furthermore, the land protrusion block may include dual circular protrusions arranged at a predetermined distance. Moreover, the land protrusion block may include a plurality of columnar (or circular) protrusions arranged at a predetermined distance.
With this configuration, even if a crack is generated and grows in any direction, the crack growth can effectively suppressed.
Moreover, the land protrusion block may include a plurality of standing plate-shaped protrusions of a predetermined width arranged at a predetermined interval and almost in parallel to one another.
With this configuration, a stress in the direction vertical to the planes of the plate-shaped protrusions can effectively suppressed by a great shear stress, thereby effectively suppressing a generation and growth of a crack.
Furthermore, the land protrusion block may include a plurality of coaxial circular protrusions having different heights in such a manner that the center protrusion is higher than the surrounding protrusions.
In this case, even a great-power crack growing over the external protrusions is stopped by the center protrusion by dispersing the crack direction. Thus, it is possible to effectively suppress growth of a great-power or small-power crack.